1. Field of the Invention
The present invention relates to orthopaedic implants, and, more particularly, to orthopaedic implants having a porous coating attached to the surface. The present invention also relates to methods for bonding coatings to substrate materials. More particularly, the present invention relates to methods for controlling a direct application of pressure for bonding porous coatings to substrate materials used in orthopaedic implants.
2. Description of the Related Art
Orthopaedic implants commonly include a metal substrate and a porous structure of a desired thickness on a bone contacting surface of the implant to promote bone growth therethrough and to enhance attachment of the implant to adjacent bone tissue. Various methods have been developed for manufacturing an orthopaedic implant having a porous surface, including plasma spraying, sintering, and diffusion bonding.
Orthopaedic implants, such as hip, knee, elbow, shoulder, and spine, for example, may include one or more porous surfaces to allow bone ingrowth for fixation. Typically, the porous materials are prepared and attached to a substrate material. The porous coatings may be pre-sintered or diffusion bonded prior to attachment to a substrate material. The porous coatings are then attached to the substrate to form a metallurgical bond with the substrate with a variety of heat treatment processes.
Contact between the substrate and the porous coating may be maintained to achieve a metallurgical bond during the entire heat treatment process. This can be achieved with fixtures formed of high temperature materials that are inert and do not react with the implant. In addition, the temperatures required to achieve a metallurgical bond are substantially high and may require the use of a vacuum furnace so that the surface of the parts are not chemically altered. The heat treatment processes utilized to achieve a metallurgical bond between the substrate and the porous coating can be approximately 14 hours with multiple iterations required. The total cycle time can be in excess of 28 hours.